15.2 Nonincremental Search

Emacs also has conventional nonincremental search commands, which require
you to type the entire search string before searching begins.

C-s <RET> string <RET>

Search for string.

C-r <RET> string <RET>

Search backward for string.

To start a nonincremental search, first type C-s <RET>.
This enters the minibuffer to read the search string; terminate the
string with <RET>, and then the search takes place. If the string
is not found, the search command signals an error.

When you type C-s <RET>, the C-s invokes incremental
search as usual. That command is specially programmed to invoke the
command for nonincremental search, search-forward, if the
string you specify is empty. (Such an empty argument would otherwise
be useless.) C-r <RET> does likewise, invoking the command
search-backward.